Method and System for Receiver Synchronization

ABSTRACT

Provided is a method for synchronizing a multiple carrier receiver to receive a transmitted signal. The method includes determining a location of one or more scattered pilot carriers in a received symbol sequence and modulating the scattered pilot carriers in accordance with a single pseudorandom binary sequence. The method also includes performing phase error correction via the modulated scattered pilot carriers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/116,532, filed Nov. 20, 2008, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to digital video broadcasting(DVB). More specifically, the present invention relates to synchronizingtransmitted data in a multi-carrier modulation based receiver used in aDVB system.

2. Background Art

DVB is the European consortium standard for the broadcast transmissionof digital terrestrial television. DVB systems transmit a compresseddigital audio/video stream, using multi-carrier modulation, such asorthogonal frequency division multiplexing (OFDM). Another popularmethod of transmitting signals is digital video broadcasting-terrestrial(DVB-T). When broadcasters employ DVB-T, the transmitted signals do nottravel via cable. Instead, they move via aerial antennas to a home basedreceiver.

DVB-T broadcasters transmit data with a compressed digital audio-videostream using a process based on a Moving Picture Expert Group (MPEG)-2standard. These transmissions can include all kinds of digitalbroadcasting, including high definition television (HDTV). MPEG-2signals represent an improvement over the older analog signals, whichrequire separate streams of transmission.

By way of background, in multi-carrier systems, such as OFDM systems,serially-inputted symbol streams are divided into unit blocks. Thesymbol streams of each unit block are converted into N number ofparallel symbols. After the conversion, these symbols, which includedata, are multiplexed and added by using a plurality of sub-carriershaving different frequencies, respectively, according to an Inverse FastFourier Transform (IFFT) technique, and are transmitted via the channelin time domain.

In addition to data, these OFDM symbols also include scattered pilotcarriers (SPC), continuous pilot carriers (CPC), and reserve tone pilotcarriers. These pilot carriers (signals) are used for framesynchronization, frequency synchronization, time synchronization,channel estimation, transmission mode identification, and/or phase noisetracing. The data and the pilot carriers constitute the useful part ofthe OFDM symbol. As understood by those of skill in the art, these OFDMsymbols also include less useful portions, such as a guard interval.

Once the OFDM symbols are captured on a receiver side of the OFDMsystem, they must be demodulated. OFDM demodulation procedures include,for example, a Fast Fourier Transform (FFT) step, an equalizing andde-interleaving step, and a synchronizing step, among others.

Synchronization of OFDM receivers is performed to locate the useful partof each symbol to which the FFT is to be applied. This synchronization,generally performed in the time domain, can be characterized as coarsesynchronization (e.g., initially performed during an acquisition period)and fine synchronization. Fine synchronization improves upon the resultsachieved during coarse synchronization enough to provide reliabledemodulation.

Current techniques for carrier and symbol synchronization during theacquisition period are time-domain based. They also, however, include asignificant frequency domain component. That is, although thesetechniques are primarily time-domain based, portions are performed afterapplication of the FFT. This time domain focus, however, necessitatesthe use of continuous pilots in order to successfully perform carrierand symbol synchronization.

The time domain component of these traditional techniques does notaccommodate the performance of fine frequency offset estimation.Therefore, traditional techniques must perform fine frequency offsetestimation in frequency domain. This is achieved by using continuouspilots. It is desirable, however, to perform all aspects ofsynchronization, including fine frequency offset estimation, in the timedomain. Time domain is preferred because it allows for much fastersignal acquisition since many more time-consuming steps (such as theestimation of the FFT window) are required before an FFT can beperformed.

It is known by those of skill in the art that coarse synchronization canbe performed in the time domain. Performing fine synchronization in timedomain, however, is not so easily accomplished. Performing finesynchronization in time domain is desirable because of the faster signalacquisition and step reduction advantages noted above. Achieving finesynchronization in the time domain, however, is difficult without theuse of the continuous pilots.

One proposed solution for performing fine synchronization in time domainhas been to use scattered pilots instead of continuous pilots to performthe phase error correction. That is, pseudorandom sequences are providedto modulate scattered pilots which in turn can be used in a separateprocess in the time domain. However, for multi-carrier systems that usemultiple sized FFTs (such as DVB-T2), using pseudorandom sequences inthis manner would add extra complexity to the receiver due to the needto receive and process multiple sequences of different sizes.

What is needed, therefore, is an improved pilot sequence structure thatcan facilitate more efficient receiver synchronization to decrease thecomplexity of receivers for multi-FFT size specifications. Particularly,what is needed is an improved technique for performing receiversynchronization using a single pilot sequence in time domain.

BRIEF SUMMARY OF THE INVENTION

Consistent with the principles of the present invention as embodied andbroadly described herein, the present invention includes a method forsynchronizing a multiple carrier receiver to receive a transmittedsignal. The method includes determining a location of one or morescattered pilot carriers in a received symbol sequence and modulatingthe scattered pilot carriers in accordance with a single pseudorandombinary sequence. The method also includes performing phase errorcorrection via the modulated scattered pilot carriers.

OFDM systems contain both continuous and scattered pilots. For commonphase error correction, continuous pilots are used as discussed above.In the present invention, however, instead of using continuous pilotsfor phase error correction, a modulated scattered pilot sequence is usedto enable the performance of both coarse and fine synchronization in thetime domain. That is, the continuous pilots can be used to assist andperform fine synchronization in time domain, ultimately reducingreceiver complexity.

However, tracking the location of scattered pilots for use in phaseerror correction can be problematic. That is, scattered pilots are notlocated in the same carrier index in each symbol. Therefore, to usescattered pilots as a substitute for continuous pilots for phase errorcorrection, one needs to know the actual scattered pilot symbol indexor, alternatively, wait for a complete cycle of scattered pilots. Thepresent invention provides an approach to resolving this issue bysubstituting a Gold sequence, with good autocorrelation properties, inthe place of the traditional pseudorandom sequence. Use of the Goldsequence enables synchronization to be achieved completely in the timedomain.

Further embodiments, features, and advantages of the present invention,as well as the structure and operation of the various embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the relevant art(s) to makeand use the invention.

FIG. 1 is a block diagram illustration of a conventional OFDM basedDVB-T system;

FIG. 2 is a graphical illustration of an exemplary pilot patternsequence;

FIG. 3 is an illustration of an exemplary linear feedback shiftregister;

FIG. 4 is an illustration of a two symbol time duration sequence;

FIG. 4B is an illustration of an exemplary linear feedback shiftregister modified in accordance with the present invention; and

FIG. 5 is an exemplary flowchart of a method of practicing an embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of the present invention refers tothe accompanying drawings that illustrate exemplary embodimentsconsistent with this invention. Other embodiments are possible, andmodifications may be made to the embodiments within the spirit and scopeof the invention. Therefore, the detailed description is not meant tolimit the invention. Rather, the scope of the invention is defined bythe appended claims.

It would be apparent to one of skill in the art that the presentinvention, as described below, may be implemented in many differentembodiments of software, hardware, firmware, and/or the entitiesillustrated in the figures. Any actual software code with thespecialized control of hardware to implement the present invention isnot limiting of the present invention. Thus, the operational behavior ofthe present invention will be described with the understanding thatmodifications and variations of the embodiments are possible, given thelevel of detail presented herein.

FIG. 1 is a block diagram illustration of transmission/receptionterminals of a conventional OFDM mobile communication system. In FIG. 1,an OFDM based mobile communication system includes a transmissionterminal 100 and a reception terminal 150. The transmission terminal 100includes a data transmitter 102, a coder 104, a symbol mapper 106, aserial to parallel (S/P) converter 108, a pilot symbol inserter 110, aninverse fast Fourier transform (IFFT) unit 112, a parallel to serial(P/S) converter 114, a guard interval inserter 116, a digital-to-analogconverter (D/A converter) 118, and a radio frequency (RF) processor 120.

In the transmission terminal 100, the data transmitter 102 generates andoutputs user data bits and control data bits to be transmitted to thecoder 104. The coder 104 receives and codes the signals output from thedata transmitter 102 according to a predetermined coding scheme, andthen outputs the coded signals to the symbol mapper 106. The coder 104may perform coding by means of a convolutional coding scheme or a turbocoding scheme having a predetermined coding rate. The symbol mapper 106modulates the coded bits output from the coder 104 according to acorresponding modulation scheme, thereby generating modulation symbols,and outputs the modulation symbols to the S/P converter 108. Themodulation scheme the symbol mapper 106 may follow includes, e.g., aBPSK (binary phase shift keying) scheme, a QPSK (quadrature phase shiftkeying) scheme, a 16QAM (quadrature amplitude modulation) scheme, 64QAMscheme, or others.

The S/P converter 108 receives and converts the serial modulationsymbols output from the symbol mapper 106 into parallel modulationsymbols, and outputs the converted parallel modulation symbols to thepilot symbol inserter 110. The pilot symbol inserter 110 inserts pilotsymbols into the converted parallel modulation symbols output from theS/P converter 108 and then outputs them to the IFFT unit 112.

The IFFT unit 112 receives the signals output from the pilot symbolinserter 110, performs N-point IFFT for the signals, and then outputsthem to the P/S converter 114. The P/S converter 114 receives thesignals output from the IFFT unit 112, converts the signals into serialsignals, and outputs the converted serial signals to the guard intervalinserter 116. The guard interval inserter 116 receives the signalsoutput from the P/S converter 114, inserts guard intervals into thereceived signals, and then outputs them to the D/A converter 118. Theinserted guard interval prevents interference between OFDM symbolstransmitted in the OFDM communication system. That is, the insertedguard interval prevents interference between a previous OFDM symboltransmitted during a previous OFDM symbol period and a current OFDMsymbol to be transmitted during a current OFDM symbol period.

The D/A converter 118 receives the signals output from the guardinterval inserter 116, converts the signals into analog signals, andoutputs the converted analog signals to the RF processor 120. The RFprocessor 120 includes a filter and a front end unit. The RF processor120 receives the signals from the D/A converter 118, RF-processes thesignals, and then transmits the signals over the air through a transmitantenna. The reception terminal 150 is discussed in greater detailbelow.

The reception terminal 150 includes an RF processor 152, ananalog-to-digital converter (A/D converter) 154, a guard intervalremover 156, a S/P converter 158, an FFT) unit 160, a pilot symbolextractor 162, a channel estimator 164, an equalizer 166, a P/Sconverter 168, a symbol demapper 170, a decoder 172, and a data receiver174.

The signals transmitted from the transmission terminal 100 pass throughmulti-path channels and are received by a receive antenna of thereception terminal 150 in a state in which noise is included in thesignals. The signals received through the receive antenna are inputtedto the RF processor 152, and the RF processor 152 down-converts thereceived signals into signals of an intermediate frequency (IF) band,and then outputs the IF signals to the A/D converter 154. The A/Dconverter 154 converts the analog signals output from the RF processor152 into digital signals and then outputs the digital signals to theguard interval remover 156.

The guard interval remover 156 receives the digital signals converted byand output from the A/D converter 154, eliminates guard intervals fromthe digital signals, and then outputs them to the S/P converter 158. TheS/P converter 158 receives the serial signals output from the guardinterval remover 156, converts the serial signals into parallel signals,and then outputs the parallel signals to the FFT unit 160. The FFT unit160 performs N-point FFT on the signals output from the P/S converter158, and then outputs them to both the equalizer 166 and the pilotsymbol extractor 162. The equalizer 166 receives the signals from theFFT unit 160, channel-equalizes the signals, and then outputs thechannel-equalized signals to the P/S converter 168. The P/S converter168 receives the parallel signals output from the equalizer 166,converts the parallel signals into serial signals, and then outputs theconverted serial signals to the symbol demapper 170.

As indicated, the signals output from the FFT unit 160 are also inputtedto the pilot symbol extractor 162. The pilot symbol extractor 162detects pilot symbols from the signals output from the FFT unit 160 andoutputs the detected pilot symbols to the channel estimator 164. Thechannel estimator 164 performs channel estimation using the pilotsymbols and outputs the result of the channel estimation to theequalizer 166. Here, the reception terminal 150 generates channelquality information (CQI) corresponding to the result of the channelestimation and transmits the CQI to the transmission terminal 100through a CQI transmitter (not shown).

The symbol demapper 170 receives the signals output from the P/Sconverter 168, demodulates the signals according to a demodulationscheme corresponding to the modulation scheme of the transmissionterminal 100, and then outputs the demodulated signals to the decoder172. The decoder 172 decodes the signals from the symbol demapper 170according to a decoding scheme corresponding to the coding scheme of thetransmission terminal 100 and outputs the decoded signals to the datareceiver 174.

In OFDM systems, data is transmitted and received via multiple carrierfrequencies. In some OFDM systems, by way of example, there can beapproximately 128 independent OFDM sub-carriers (i.e., tones) thatoccupy the available bandwidth. In these systems, data is modulated andtransmitted via many of these subcarriers. Approximately 10 of thesub-carriers do not necessarily carry information. These subcarriers,also referred to as pilot tones, can be used to guard the informationcarrying subcarriers, to simplify the filtering requirements of thesystem, or to provide reference phase/amplitude information for thedemodulator. The positions of the pilot tones may be defined accordingto the communication standard or defined by the user/designer of thesystem. Some pilot tones are located on two ends of the frequencyspectrum and some of the pilot tones are interspersed within thefrequency spectrum.

For each transmitted carrier signal, an OFDM receiver normally attemptsto compensate for the distortion induced by the transmission channel.This will normally involve a channel estimation operation and a channelcompensation operation. To assist a receiver in overcoming multipathdistortion, pilot signals with known data patterns are transmitted. Thepilot tones are used to support channel estimation operations. Thesechannel estimation operations normally attempt to estimate the amplitudeand phase distortion introduced by the communications channel.

The pattern structure of the pilot tones can be in essentially anymanner, provided that the Nyquist sampling criteria for thecommunication channel's impulse response and rate of change aresatisfied. The number of pilot tones transmitted is often a function ofthe expected multipath distortion delay and the anticipated rate ofchange in channel conditions. However, for purposes of efficiency, it isdesirable to minimize the number of pilot tones transmitted since thetransmission of a pilot tone precludes the transmission of data in thetransmission slot used to transmit the pilot tone.

DVB-T OFDM systems often use their pilot tones for the purpose of makingchannel estimation easier. However, the sparseness of these tonesrenders it difficult to estimate the channel quickly and with efficientmemory usage and calculations.

Channel estimation is an important function for modern wirelessreceivers. With even a limited knowledge of the wireless channelproperties, a receiver can gain insight into the information sent by thetransmitter. The goal of channel estimation is to measure the effects ofthe channel on known, or partially known transmissions. A channel canchange channel properties due to changing conditions and topology. OFDMsystems are especially suited for estimating these changing channelproperties. More specifically, in OFDM systems, the subcarriers areclosely spaced and the system is generally used in high speedapplications that are capable of computing channel estimates withminimal delay. As noted above, subcarriers that are sent with a knownpower and make-up are called pilots and are used for synchronization.

The present invention provides a unique and novel approach to performingchannel estimation. More particularly, the present invention providesenhancements to known channel estimation techniques, such as tonereservation. In tone reservation, for example, carriers are reserved andpopulated with arbitrary values in order to decrease the PAPR.

The present invention is illustrated in the following example. Assumethat non-arbitrary values can be chosen for carriers that are known.That is, in a given symbol, for example, carriers 3, 7, and 10 areavailable and instead of using arbitrary values for each of thesecarriers, five non-arbitrary values (e.g., −2, −1, 0, 1, and 2) can beused. Thus, in this example there are 125 choices (i.e., 5³). Assumethat each of the 125 choices includes sufficient granularity such thatthe peak to average power ratio (PAPR) could be decreased by an amountcomparable to PAPR reduction using the arbitrary values. In thisscenario, the PAPR could be reduced almost as much as it could by usingthe arbitrary values. By using small sets of non-arbitrary values,however, the receiver has more information with which to perform channelestimates and equalization. The ability to provide this information tothe receiver enables these carries to be used as pilots.

Traditionally, only dedicated pilots could be used to provide channelestimates. The present invention enables additional, non-pilot channelcarriers, to be used to provide the channel estimates.

FIG. 2 is a graphical illustration of an exemplary pilot patternsequence 200. The pilot pattern sequence 200 includes a symbol group 202of nine OFDM symbols arranged along Y axis 204 representative of time.The Y axis 204, for example, can be in gradations of 200 microseconds(μs) up to 1 millisecond. The fidelity of these gradations is dependentupon the total duration of each of the OFDM symbols.

The graph of FIG. 2 also includes X axis 206 representative offrequency. Evenly spaced carries in each of the symbol groups arearranged along the X axis 206.

In FIG. 2, each of the symbols within the symbol group 202 includesdifferent carrier types comprising data carries (d_(ij)), reserved tones(r_(ij)), continuous pilots (c_(ij)), and scattered pilots (s_(ij)).Although the pilot sequence 200 is representative of a sequenceconfigured for use in a DVB-T2 system, it can apply to any OFDM system.

The first element in the carrier type subscript (e.g. d_(ij)) representsa carrier index. The second element of the subscript represents a timeindex. For example, in FIG. 2, a first OFDM symbol 207, occurring attime 0, includes a continuous pilot c_(0,0), a data carrier d_(1,0), adata carrier d_(2,0), etc.

In an OFDM symbol, the data carriers are representative of actualtransmitted data. The continuous pilots and the scattered pilots areprovided to be able to perform channel estimation. For the symbol 207,the continuous pilots are c_(0,0), and c_(0,15). The symbol 207 alsoincludes a scattered pilot s_(12,0). The notion of why two differenttypes of pilots are used is well understood by those of skill in the artand will not be discussed herein.

Focusing on other aspects of pilots tones, most OFDM systems include theconcept of having pilots that are not located within any particularsystem. For example, in the symbol group 202, all of the continuouspilots have a carrier index identical to other carrier pilots, meaningthey are in vertical columns with other continuous pilots. For example,there are continuous pilots at carrier index “0” and carrier index “15.”The fact that the continuous pilots are all vertically aligned indicatesthe pilot location stays the same, across different symbols. That is, ifcarrier 0 is a pilot in symbol 0 (i.e., symbol 207), then carrier 0 isalso a pilot in a symbol 208, and a pilot in symbol 210, etc. Thisprocess is typical of DVB-T systems and wireless local area network(LAN) systems.

The problem, however, with pilot configurations such as theconfiguration of FIG. 2 is that the density of the continuous pilots istypically insufficient to adequately perform channel estimation. Tocompensate for this lack of continuous pilot density, roving or“scattered” pilots are provided to augment the channel estimationcapability of the continuous pilots. In FIG. 2, as discussed above, inthe symbol 207 the scattered pilot is denoted as s_(12,0). The symbol208 includes a scattered pilot s_(9,1) etc. These are the typical typesof pilots that can be found in conventional OFDM systems.

As noted above, the all of the pilot carriers are evenly spaced alongthe X axis 206. In traditional OFDM systems, the value of these pilotcarriers is derived from the output of a linear feedback shift register(LFSR). More specifically, an LFSR is used to produce a pseudorandombinary sequence (PRBS). The PRBS includes a series of binary values andis used to modulate reference information ultimately transmitted in theform of continuous and scattered pilots. Thus, the output of the LFSR isused to determine the value(s) of the continuous and scattered pilots.This technique is used, for example, in current (DVB-T) systemsdiscussed above.

FIG. 3 is an illustration of an exemplary LFSR 300 that can be used toproduce a PRBS in accordance with the present invention. By way ofexample, the LFSR 300 is a component within the pilot symbol inserter110, illustrated in FIG. 1.

As known to those of skill in the art randomly generated sequences arenot entirely random. That is, all randomly generated sequenceseventually repeat themselves over time. For example, a sequence of100110001, output from the LFSR 300, would repeat over time. If, inaddition to the repeatability aspect of the PRBS, additional propertiesof the PRBS could be known or predicted, more clever techniques can beused to aid the receiver in performing synchronization. More clevertechniques would ultimately make the synchronization process moreefficient and permit simpler OFDM receiver designs.

Use of the PRBS in deriving values for the continuous and scatteredpilot sequences requires computation of auto and cross correlations ofthe pilot samples. Those sequences that have good auto and crosscorrelation properties are the best choices for pilot sequences. Forexample, the autocorrelation of a typical PRBS can be computed in thebinary domain. If the autocorrelation resembles an impulse function inthe binary domain (i.e., suggesting that there is only one high non-zerovalue and the remaining values are very low non-zero values), then thisparticular autocorrelation computation can be used to at least determinewhen the sequence began within the received symbol. Knowing when thesequence began in the received symbol is useful in speeding theacquisition and synchronization process, and minimizing the occurrenceof symbol ambiguities.

A variant of the PRBS autocorrelation technique above has been used inmulti-carrier systems for years, being applied, however, only in timedomain. The present invention can be applied in OFDM based systems infrequency domain. That is, embodiments of the present invention computethe autocorrelation of the PRBS in the binary field and not on actualnumbers. Time domain autocorrelation performed over real/complex numbersdoes not translate easily to a PRBS in the frequency domain. The presentinvention is formulated upon the concept that a “good” long PRBS in thebinary domain (which is easy to find) works well after transformation toreal/complex numbers via modulation.

FIG. 4 is a graphical illustration 400 of two OFDM symbols, combine torepresent two symbol durations in time. More specifically, in theillustration 400, a first group of multi-carrier symbols 402 and asecond group of multi-carrier symbols 404 are shown. The first group 402includes symbols 0 to 9, each having a 1^(st) symbol duration of time406. The second group of symbols 404 includes a 2^(nd) symbol durationtime 408. The first group of symbols 402 can include 1704 individualcarriers, such as the carriers 410, if the OFDM system operates in the2K mode. The first group of symbols 402 will include 6816 carriers,however, if the 8K mode is used.

In the present invention, the pseudorandom sequence used to derive thescattered and pilot carrier sequences is desirably at least twice aslong as any transmitted symbol (i.e. at least two symbols duration). Ifat least twice as long as the transmitted symbol, symbol ambiguities canbe more easily resolved. For example, if a particular sequence is onlysix values long, embodiments of the present invention provide theability to determine any errors to within, for example, ± three values.

In OFDM systems designed in accordance with the present invention, aGold sequence is used. That is, to create a PRBS in accordance with thepresent invention, an LFSR, such as the LFSR 300, can be configured toproduce a Gold sequence (with good autocorrelation properties) insteadof the traditional PRBS used in conventional OFDM systems.

As understood by those of skill in the art, a Gold sequence includes2^(m)+1 sequences each one with a period of 2^(m)−1. This Gold sequenceis desirably at least as long as the complete scattered pilot cycle thatis used, or at least two symbols duration 412. In this manner,syhcnronization can be achieved completely in the time domain with onlytwo symbols wait in the time domain. More specifically, across-correlation of the received data with the FFT of the modulatedGold sequence over a time period of two symbols immediately provides anidentifiable peak in the output that indicates where the symbol begins.

The cost to produce this Gold sequence is simply the programming oraddition of two more bits in the LFSR to generate the sequence. Two morebits in the LFSR can be produced by modifying the LFSR 300 of FIG. 3. Amodified version of the LFSR 300 is shown in FIG. 4B.

In FIG. 4B, the LFSR 302 (e.g., a modified version of the LFSR 300) canbe produced by adding two more 1-bit delay blocks, such as the 1-bitdelay blocks 304 and 306 of extended module 308. In simpler terms, thepresent invention permits reusing a longer sequence, configured for usewith the largest FFT size, with smaller FFT sizes, thereby decreasingthe number of LFSRs that have to be created. This approach ultimatelysimplifies the receiver.

Embodiments of the present invention are particularly applicable toDVB-T systems. Most digital television standards that are based on OFDMhave multiple FFT sizes. That is, the number of carriers in one symbolcould either be 2000 carriers (2K mode), or roughly 8000 (8K mode). Inconventional OFDM systems, in order to resolve all the ambiguitieswithin one symbol, the PRBS sequence must be as long as the length ofone symbol. Using this conventional approach, however, a different LFSRwould be required for each FFT size in the receiver chip.

In the present invention, the pseudorandom sequence (e.g., Gold code) isdesigned to be long enough such that its receiver correlation can occurover multiple symbols (i.e., twice as long as a single symbol),permitting the same sequence to be used for all the OFDM FFT sizes.

Desirably, the sequence length should be twice as long as the number ofactive carriers in the largest FFT size. For shorter FFT sizes, thesequence length will be greater than twice the corresponding number ofactive carriers. For the shorter FFT sizes, however, this longersequence does not slow down synchronization because the largest FFT sizeis the only one tested. The results for all smaller FFT sizes fall outas side information, thus precluding the need for testing the smallerFFT sizes.

FIG. 5 is a flowchart of an exemplary method 500 of practicing anembodiment of the present invention. In FIG. 5, a step 502 includesdetermining a location of one or more scattered pilot carriers in areceived symbol sequence and modulating the scattered pilot carriers inaccordance with a single pseudorandom binary sequence, as indicated in astep 504. In step 506, phase error correction is performed via themodulated scattered pilot carriers.

The present invention may be embodied in hardware, software, firmware,or any combination thereof. Embodiments of the present invention orportions thereof may be encoded in many programming languages such ashardware description languages (HDL), assembly language, C language, andnetlists etc. For example, an HDL, e.g., Verilog, can be used tosynthesize, simulate, and manufacture a device, e.g., a processor,application specific integrated circuit (ASIC), and/or other hardwareelement, that implements the aspects of one or more embodiments of thepresent invention. Verilog code can be used to model, design, verify,and/or implement a processor that can scale frames using content-awareseam carving.

For example, Verilog can be used to generate a register transfer level(RTL) description of logic that can be used to execute instructions sothat a frame can be scaled using content-aware seam carving. The RTLdescription of the logic can then be used to generate data, e.g.,graphic design system (GDS) or GDS II data, used to manufacture thedesired logic or device. The Verilog code, the RTL description, and/orthe GDS II data can be stored on a computer readable medium. Theinstructions executed by the logic to perform aspects of the presentinvention can be coded in a variety of programming languages, such as Cand C++, and compiled into object code that can be executed by the logicor other device.

Aspects of the present invention can be stored, in whole or in part, ona computer readable media. The instructions stored on the computerreadable media can adapt a processor to perform the invention, in wholeor in part, or be adapted to generate a device, e.g., processor, ASIC,other hardware, that is specifically adapted to perform the invention inwhole or in part. These instructions can also be used to ultimatelyconfigure a manufacturing process through the generation ofmaskworks/photomasks to generate a hardware device embodying aspects ofthe invention described herein.

Conclusion

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or morebut not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

The claims in the instant application are different than those of theparent application or other related applications. The Applicanttherefore rescinds any disclaimer of claim scope made in the parentapplication or any predecessor application in relation to the instantapplication. The Examiner is therefore advised that any such previousdisclaimer and the cited references that it was made to avoid, may needto be revisited. Further, the Examiner is also reminded that anydisclaimer made in the instant application should not be read into oragainst the parent application.

1. A method for synchronizing a multiple carrier receiver to receive atransmitted signal, comprising: determining a location of one or morescattered pilot carriers in a received symbol sequence; modulating thescattered pilot carriers in accordance with a single pseudorandom binarysequence; and performing phase error correction via the modulatedscattered pilot carriers.
 2. The method of claim 1, further comprisingdetermining a location of one or more continuous pilot carriers; andperforming coarse and fine synchronization using the continuous pilotcarriers.
 3. The method of claim 2, wherein the coarse and finesynchronization are performed in time domain.
 4. The method of claim 1,wherein a duration of the single pseudorandom binary sequence is atleast two symbols.
 5. The method of claim 1, wherein the pseudorandomsequence is a Gold code.
 6. The method of claim 1, wherein themulti-carrier receiver operates in accordance with orthogonal frequencydivision multiplexing (OFDM) principles.
 7. A computer program productincluding a computer readable medium storing program code, which whenexecuted are adapted to enable a processor to: determine a location ofone or more scattered pilot carriers in a received symbol sequence;modulate the scattered pilot carriers in accordance with a singlepseudorandom binary sequence; and perform phase error correction via themodulated scattered pilot carriers.
 8. A computer program product ofclaim 7, further comprising determining a location of one or morecontinuous pilot carriers; and perform coarse and fine synchronizationusing the continuous pilot carriers.
 9. A computer program product ofclaim 8, wherein the coarse and fine synchronization are performed intime domain.
 10. A computer program product of claim 7, wherein aduration of the single pseudorandom binary sequence is at least twosymbols.
 11. A computer program product of claim 7, wherein thepseudorandom sequence is a Gold code.
 12. A computer program productaccording to claim 7, wherein the multi-carrier receiver operates inaccordance with orthogonal frequency division multiplexing (OFDM)principles.
 13. The computer program product of claim 7, wherein theprogram code comprises instructions in a hardware description language.14. The computer program product of claim 13, wherein the instructions,when executed, configure a manufacturing process to manufacture aprocessor adapted to determine a location of said scatter pilot carriersand perform said phase error correction.
 15. The computer programproduct of claim 14, wherein said instructions are adapted to generatephotomasks, said photomasks employed to configure said manufacturingprocess.
 16. A receiver configured to operate in an orthogonal frequencydivision multiplexing (OFDM) system, comprising: a processor todetermine a location of one or more scattered pilot carriers in areceived symbol sequence; a modulator to modulate the scattered pilotcarriers in accordance with a single pseudorandom binary sequence; andan error correction block to perform phase error correction via themodulated scattered pilot carriers.
 17. The receiver of claim 16,further comprising determining a location of one or more continuouspilot carriers; and means for performing coarse and fine synchronizationusing the continuous pilot carriers.
 18. The receiver of claim 17,wherein the coarse and fine synchronization are performed in timedomain.
 19. The receiver of claim 16, wherein a duration of the singlepseudorandom binary sequence is at least two symbols.